This invention relates to an art of heat exchangers for automobiles such as evaporators, condensers, radiators, etc.
Heat exchangers made of aluminum or an aluminum alloy material (hereinafter simply referred to as Al material) are manufactured through a steps of forming tubes or fins using brazing sheets clad with brazing materials, assembling them in a predetermined shape and brazing them.
However, it is difficult to manufacture brazing sheets and the yield is low, so that this method is wasteful. In addition, waste processing thereof is costly because brazing sheets are not suitable for recycling. Furthermore, it needs special techniques to manufacture tubes using brazing sheets. Also, brazing sheets are difficult to be processed to a fin shape and apt to damage jigs. In addition, brazing sheets are difficult to be processed so as to be thin, so that it is also difficult to produce small and light heat exchangers.
By the way, as a brazing material for brazing sheets, an Al--Si alloy is used (Japanese Patent Publication No.27037 (1983)).
In addition, as another brazing material, Al--Si--Zn alloy is known (Japanese Patent Publication No.27037 (1983), Japanese Patent Laid-Open No.151188 (1991)). The method of manufacturing brazing sheets by cladding a brazing material made of Al--Si--Zn alloy thereon, however, is difficult, so that this method is not used in practice.
Moreover, when using Al--Si alloy as a brazing material, it is proposed to provide a Zn film thereon in advance with a means such as flame spray coating, etc. for increasing the corrosion resistance. Namely, this implies that a fin and a tube on which an Zn film is provided are brazed with the Al--Si alloy clad on the fin. But, this method includes complicated steps such as the step of providing a Zn film, so that this method is not preferable.
Like this, in the prior art, when trying to keep a sufficient corrosion resistance, the manufacturing process becomes complicated and wasteful. Contrary to this, if trying to reduce manufacturing cost, the corrosion resistance goes down.